Conventional solar cells are able to deliver electrical energy only when the cells are illuminated. Also, the output of electric current from the cells directly changes with light intensity. These characteristics create challenges in the real-world implementation of solar cells because no power can be generated at night and temporary blockages of sunlight (e.g., because of passing clouds) result in sudden changes in the output current.
Because of these limitations, external energy storage devices, such as batteries or supercapacitors, are required for conventional solar cell applications. While such energy storage devices address the limitations of conventional solar cells, they create other problems. For example, having to associate solar cells with independent energy storage devices reduces the overall energy conversion efficiency of the solar energy system. In addition, the limited lifetime of and the maintenance requirements for the energy storage devices increase the costs of the solar energy systems. Furthermore, systems that use batteries may not be environmentally friendly.
In view of the above discussion, it can be appreciated that it would be desirable to have a solar energy system that does not require independent energy storage devices.